1. Field of the Invention
This invention relates to a photographic light-sensitive silver halide element, particularly an element intended for exposure by use of laser light, and more particularly to a photographic light-sensitive silver halide element which is intended for exposure through a contact screen by use of laser light to form dot images.
2. Description of the Prior Art
In printing an image having continuous gradation, as is well known in the art, the image is broken up into small dots, varying in size according to the density thereof, and is converted into a so-called dot image. Such a dot image is produced by applying onto a high contrast light-sensitive element, e.g., a lithographic film, a photographic exposure through a contact screen or glass screen.
Light sources which have heretofore been used for the application of a photographic exposure through a contact screen to produce such dot images include a tungsten lamp, a mercury lamp, a xenon lamp, a glow lamp, etc.
Recently an image-forming method according to the so-called scanner system has been increasingly used, in which according to an image signal obtained by scanning an original image having continuous gradation, an exposure is applied onto a photographic light-sensitive silver halide element to produce a negative or positive image corresponding to the original image. This image-forming method of the scanner system includes the use of a dot generator system in which a dot generator is used, and the so-called screen scanner system in which the dot image is obtained by use of the contact screen, as described above.
As a light source for use in the dot image-forming method of the scanner system, the light sources as described above, e.g., a tungsten lamp, are not suitable, because of their relatively poor outputs and short lives. Recently, therefore, a scanner has been developed in which coherent laser light is used as the exposure light source.
For the generation of laser light, ruby, neon-helium gas, argon gas, krypton gas, helium-cadmium gas, carbon dioxide gas, etc., laser materials are used. Of these, the neon-helium gas is relatively inexpensive, and produces a stable output, therefore it is widely used.
In order to apply a photographic exposure through a contact screen onto a light-sensitive element, e.g., a lithographic film, to form a dot image, it is necessary to bring the contact screen into intimate contact with the light-sensitive element, for example, by a vacuum-contacting method.
When light enters the interface between two different members in close contact with each other, an interference phenomenon of light occurs. This phenomenon is well known as Newton's Rings. Therefore, when a high contrast light-sensitive element is exposed through a contact screen, this interference phenomenon of light occurs in the interface between the screen and the light-sensitive element, causing a striped pattern (hereinafter referred to as the "interference fringe") to be formed in the light-sensitive element.
In particular, when laser light is used as the light source, the characteristic properties of laser light, i.e., that it is coherent and has a uniform phase, the interference phenomenon is intensified, as a result of which the interference fringe appears more strongly.
When the interference occurs in a pattern having a dot area of about 10% to 20% of the area wherein the dots are scattered, e.g., photographs of a clear sky and electric articles having pale colors, the interference fringe is printed as is and appears in the printed image, and it cannot be retouched. When the interference fringe occurs in a pattern having a dot area of about 50%, e.g., a portrait, a contour line-like pattern is formed in the printed image, leading to a serious defect in the dot image.
Therefore, minimizing the occurrence of interference fringe in a method of producing a dot image in a high contrast light-sensitive element by applying a photographic exposure thereto through a contact screen using a laser as the light source (e.g., a screen scanner method) has been the important subject of research by those engaged in the development of such methods.
Though it was proposed to minimize the formation of Newton's Rings using matting agents such as colloidal silica or polymethyl methacrylate, these matting agents have been found unsatisfactory for such use in a light-sensitive element intended for photographic exposure using a laser light.